With the renewal deadline on the horizon for “How I Met Your Mother,” the show’s writers need to know soon whether or not this season will be its last (ie, they need to know when to finally reveal who the heck the mother is).

Negotiations for a ninth season are underway, according to Deadline, as the contracts for the creators and the entire cast are up at the end of the season.

The “HIMYM” creators are pressing for a decision on the show’s fate by the end of December, so they can set in motion how to wrap-up the long-running mystery of the sitcom and properly play out the big reveal in a satisfying way for fans who’ve waited eight long seasons now to learn the identity of the mother of Ted’s (Josh Radnor) kids.

Bearing that in mind, talks are now heating up between CBS, 20th Century Fox TV (who produces the series), creators Craig Thomas and Carter Bays, and reps for the core ensemble cast of Josh Radnor, Colbie Smolders, Neil Patrick Harris, Alyson Hannigan and Jason Segel.

As of late summer, CBS had said they were optimistic about the show being renewed for another season: “We want the show to come back next year,” said CBS entertainment president Nina Tassler, according to Deadline. “We’re not there yet in terms of resolving the situation, but we’re pretty optimistic.”

But one sticking point could be a loose end among the cast. The creators have previously indicated they “never ever” want to move forward without the full cast on board, but since the series launched in 2005, cast member Jason Segel’s movie career (“Forgetting Sarah Marshall,” “Knocked Up,” “This Is 40″) has taken off.

The Deadline story quotes sources saying, “Segel has indicated that it is unlikely for him to return,” although the actor has not officially said no to the possibility.

We’re guessing CBS will do whatever it takes to secure one more year to give the story of “How I Met Your Mother” a proper send-off, with or without Marshall (Segel) in the mix. After all, this is the same network that managed to salvage “Two and a Half Men” after the Charlie-Sheen apocalypse, as the article points out. But if renewal negotiations were to fall through, “HIMYM” will be forced to wrap up production in a hurry.